1. Field of the Invention
The present invention relates to an ink jet printing apparatus including a unit for recovering a function of a nozzle defined as an ink discharge member of an ink jet head for printing a print image by jetting ink liquid droplets.
2. Related Background Art
In recent years, a resolution of an ink jet printing apparatus has increasingly been enhanced. The resolution, which was hitherto on the order of 180 dpi, increases up to 360 dpi and further to 600 dpi more than three times as high as the above. The resolution is thus increased, which turns ink liquid droplets into much finer liquid droplets and further enhances a density of a nozzle arrangement. With this higher resolution, a variety of control operations and works have been implemented with respect to nozzle members defined as ink discharging portions of the ink jet printing apparatus in order to obtain a discharge stability. For example, when the printing ceases for a long period of time, a nozzle surface is capped so as not to unnecessarily evaporate the water content from an ink liquid in the nozzle member. This prevents the ink from being unable to be discharged due to an increase in viscosity of the ink liquid in the nozzle member and a composite factor such as a fixation of the ink adhered to the periphery of the nozzle, an adhesion of dusts and the increased viscosity of the ink in the nozzle member. Further, there is conducted an operation of sucking the ink liquid within the nozzle. A first purpose of this operation is to forcibly remove the ink liquid of which the viscosity increases at the nozzle if the ink jet printing apparatus has been in an unused state for a long time. A second purpose of the operation described above is to remove bubbles existing inside the ink liquid in the nozzle member. Moreover, the nozzle surface is exposed directly to the atmospheric air during the printing process, and therefore the viscosity of the ink liquid increases on the nozzle surface. Then, a discharge resistance rises due to the ink layer having the increased viscosity, with the result that the liquid droplets can not be discharged with a stability. Further, for obviating an increased concentration of a color ink liquid due to the increased viscosity of the ink, the ink is discharged when starting the print and during the printing, thereby obtaining the stable discharge (which operation is referred to as a preliminary discharge). A variety of nozzle recovering operations based on the method described above have hitherto been carried out, however, particularly a preliminary discharging method of discharging the ink liquid droplets into a cap for the preliminary discharge at an interval of a fixed time by way of the nozzle recovering operation during the printing, is conceived as a quite important nozzle recovering method. In a serial ink jet printing apparatus having a plurality of nozzle rows consisting of a comparatively small number of printing nozzles, e.g., approximately 128 nozzles, the preliminary discharge involves the use of a method of carrying out the preliminary discharge by moving a carriage mounted with the nozzles to a predetermined preliminary discharge position. Further, in a high-speed full-multi printing apparatus including a plurality of nozzle rows consisting of a comparatively large number of printing nozzles, e.g., approximately 5200 nozzles, with respect to an electrostatic absorption carrier in which the carrier apparatus of the printing apparatus uses a belt etc., or an air suction adsorbing method, or an intermediate transfer body system using a drum and a transfer body system, there is taken a method of effecting the preliminary discharge on a belt used for the electrostatic adsorption carrier or in an arbitrary position or a random position on the drum used in the transfer body system.
The preliminary discharge explained above presents no problem in terms of a re-usability, a disposal processing property, a preserving property and an intra-appliance dangerousness when the preliminary discharge is executed using the liquids exhibiting the same attributes, e.g., the inks of the same color stuff, the same concentration and the same chemical characteristic. However, in the case of simultaneously using the liquids having different attributes, for instance, when enhancing an image quality by use of the above liquid and a printability enhancing liquid classified as one kind of color stuff reactive substances, there might arise an inconvenience in the preliminary discharge described above. Herein, the enhancement of the printability implies an enhancement of image qualities such as a density, a saturation, a degree of sharpness of an end portion and a dot diameter etc., an enhancement of a fixing property of the ink, and an enhancement of a weatherability such as a water resistance and a light resistance, i.e., an image preserving property. Further, the term xe2x80x9cinsolublexe2x80x9d implies such a:phenomenon that the anion radical contain in a dye within the ink and the cation radical of a cation substance which is contained in the printability enhancing liquid, cause interaction ion-wise enough to produce ion-coupling, and the color stuff (dye) uniformly solved in the ink is separated from the solution. Note that according to the present invention, even if all the dyes in the ink are not necessarily dissolved, there are obtained effects such as enhancements of the density, the character quality and the fixing property. Moreover, the term xe2x80x9cagglutinationxe2x80x9d is used having the same meaning as the term xe2x80x9cinsolublexe2x80x9d when the-color stuff used in the ink is an aqueous dye containing, e.g., the anion radical. Further, if the color stuff used in the ink is a pigment, a pigment dispersant or the pigment surface and the cation radical of the cation substance which is contained in the printability enhancing liquid, cause ion-wise interaction, with the result that the pigment is brought into a dispersing destruction including an enlargement of a particle-size of the pigment. Normally, with the agglutination described above, the viscosity of the ink increases.
In the full-multi printing apparatus using the printability enhancing liquid exhibiting the performance explained above, when effecting the preliminary discharge onto the carrier belt in order to ensure a discharge reliability of the printing head, and if the printing heads for respective colors including the printing head for discharging the printability enhancing liquid onto the carrier belt execute the preliminary discharges in proper positions on the carrier belt, the ink dyes become insoluble due to the printability enhancing liquid and the ink dye as well, and a coagulation thereof occurs on the carrier belt. In general, when the coagulation described above occurs on the carrier belt, there declines a cleaning property of an ink cleaning apparatus for removing the inks on the carrier belt to prevent the inks from being transferred on the next printing paper. The decline of the cleaning property is that there decreases a quantity of the inks adsorbed to the cleaner for removing the inks adhered onto the carrier belt, and there grows a possibility of the inks being adhered to the next printing paper. Further, the adhesion of the inks onto the carrier belt, especially when the electrostatic adsorption carrier is carried out, might cause changes in dielectric constant and on volume resistivity, which in turn leads to a change in a paper adsorbing force. The change in the adsorbing force of the carrier belt changes a condition under which cockling thereof occurs, with the result that a floating quantity of the printing paper above the carrier belt varies. If the paper floating quantity increases, the printing paper is brought into contact with the printing head, which might cause a paper jam. This is considered inappropriate as the printing system.
Moreover, in a printing apparatus having an ink circulating system, a system for recovering only the liquids assuming the same color, composed of the same color stuff and having the same concentration is, not in an economic aspect, required to be structured when in the printing process or in a discharge portion protecting state.
Further, in the high-speed printing system required to execute the preliminary discharge onto the intermediate transfer body or the printing paper carrier member for maintaining the ink discharge portion, there arises a necessity for changing the cleaning materials for the preliminarily-discharged member, depending upon cleaning properties of the various inks.
It is a primary object of the present invention to obviate the problems described above.
To accomplish this object, according to a first aspect of the present invention, an ink jet printing apparatus including a plurality of heads for discharging liquids used for plural types of prints each exhibiting a different attribute, comprises a control unit for adjusting and controlling a timing of a preliminary discharge for maintaining a discharge not contributing to records by the plurality of heads, per attribute of the liquids to be discharged in such a manner that droplets of the liquids exhibiting the same attribute are discharged to the same position.
According to a second aspect of the invention, in the ink jet printing apparatus according to the first aspect, the liquids exhibiting the different attributes are an ink containing a coloring agent, and a liquid, not containing the coloring agent, for enhancing a quality of an image formed by the ink.
According to a third aspect of the invention, in the ink jet printing apparatus according to the second aspect of the invention, the head is of a serial scan type, the printing apparatus provides one of areas exceeding a printing range with a preliminary discharge position for the ink and the other area with a preliminary discharge position for the image quality enhancing liquid, and the control unit performs control in such a manner that the liquids are discharged to the corresponding positions.
According to a fourth aspect of the invention, in the ink jet printing apparatus according to the second aspect of the invention, the head is of a serial scan type, the printing apparatus provides one of areas exceeding a printing range with a preliminary discharge position for the ink and a preliminary discharge position for the image quality enhancing liquid, which is disposed adjacently to the preliminary discharge position for the ink, and the control unit controls a discharge timing in such a manner that the liquids are preliminarily discharged to the corresponding positions.
According to a fifth aspect of the invention, in the ink jet printing apparatus according to the second aspect of the invention, the head is of a serial scan type, the printing apparatus provides one of areas exceeding a printing range with a preliminary discharge position for the ink, and a discharge timing is controlled so that the ink is preliminarily discharged to the preliminary discharge position for the ink, and the image quality enhancing liquid is preliminarily discharged onto a recording medium.
According to a sixth aspect of the invention, in the ink jet printing apparatus according to the second aspect of the invention, the head is of a full-line type, the printing apparatus includes a carrier belt for carrying the recording medium, and the control unit performs control of preliminarily discharging the ink onto the carrier belt and-preliminarily discharging the image quality enhancing liquid onto the recording medium.
According to a seventh aspect of the invention, in the ink jet printing apparatus according to the sixth aspect, a unit for making the liquid discharging position coincident with each other includes a sensor for detecting an upper end of paper, a head-to-head delay counter for counting a carrier distance to a printing head with a sensor signal serving as a trigger, a paper position counter actuated with a counter signal serving as a trigger, a head-to-head delay counter for counting a carrier distance to a next printing head, a comparing circuit for comparing a signal of the paper position counter with a signal of a printing area designation register and outputting a printing signal, and a comparing circuit for comparing the signal of the paper position counter with a signal of a preliminary discharge area designation register and outputting a preliminary discharge signal.
According to an eighth aspect of the invention, the ink jet printing apparatus according to the sixth aspect of the invention further comprises a cleaning unit for cleaning the ink discharged onto the carrier belt.
According to a ninth aspect of the invention, in the ink jet printing apparatus according to the second aspect of the invention, the head is of the full-line type, the recording apparatus includes a carrier belt for carrying the recording medium, and the control unit performs control of preliminarily discharging of the image quality enhancing liquid to a first position on the carrier belt, and preliminarily discharging of the ink to a second position adjacent to the first position with a spacing therebetween.
According to a tenth aspect of the invention, the ink jet printing apparatus according to the seventh aspect of the invention further comprises a cleaning unit for cleaning the ink discharged onto the record carrier belt, the cleaning unit having a circumferential length corresponding to a distance containing a width of the first position, a width of the second position, and an adjacent spacing between the first and second positions.
According to an eleventh aspect of the invention, in the ink jet printing apparatus according to the first aspect of the invention, a recording unit for printing a printed material includes an electrothermal converting element for generating an energy for discharging the ink.
According to a twelfth aspect of the invention, in the ink jet printing apparatus according to the eleventh aspect of the invention, the ink is discharged out of a discharge port by utilizing layer boiling occurred in the ink with the thermal energy applied by the electrothermal converting element.
The constructions given above make it feasible to improve a re-usability of the inks and to maintain the cleaning function of the cleaning member for a carrier medium or a transfer medium, and to thus enhance the easiness of processing the disposal inks. Further, it is possible to reduce the costs for the ink jet printing apparatus and to hold the performance thereof.
These together with other objects and advantages which will be subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout.
Other objects and advantages of the present invention will become apparent during the following discussion in conjunction with the accompanying drawings.